1. Field of the Invention
The present invention generally relates to a sheet transport device which transports a sheet by using an electrostatic force and an image forming apparatus using the sheet transport device.
2. Description of the Related Art
As an image forming apparatus such as a printer, a facsimile, a copier, a plotter, and a multifunctional apparatus that has the above functions, for example, there is an apparatus using a liquid ejecting device having a liquid ejecting head which ejects recording liquid (ink) onto a recording medium for forming an image on the recording medium. The recording medium is not limited to a sheet, and other recording media such as an image transferring medium and recording paper can be used as the recording medium; and as the image forming, image recording, image printing, letter printing, letter transferring and so on are included.
The image forming apparatus forms an image on a recording medium formed of materials such as paper, thread, string, cloth, glass, wood, plastic, metal, and ceramics by ejecting recording liquid onto the recording medium by using an electrophotographic system or other systems. Further, the image forming includes attaching an image such as a pattern onto a recording medium in addition to attaching an image having a meaning such as a letter and a figure onto the recording medium. The recording liquid is not limited to ink and can be fluid to be ejected.
Generally, the image forming apparatus having the liquid ejecting device provides a sheet transport device including a transport belt which transports a sheet by using an electrostatic force so as to maintain flatness of the sheet.
In Patent Document 1, a transfer belt device of an image forming apparatus is disclosed. The transfer belt device provides an endless type transfer belt which is wound around plural rollers and driven by the rollers, and transports a transfer sheet from an upstream side to a downstream side of a photoconductor body by attaching the transfer sheet on the transfer belt by the electrostatic force. A driving roller in the plural rollers contacts the sheet transport surface of the transfer belt, and a cleaning member contacts the surface of the driving roller. The cleaning member is held by a holding member which is a part of a case, and the holding member is detachably attached to the case.
[Patent Document 1] Japanese Patent No. 3487715 (Japanese Laid-Open Patent Application No. 9-292783)
Since the transport belt in the belt transport device always contacts a charging member (charging unit), liquid such as ink may be attached onto the transport belt and a water droplet when dew condensation occurs may be attached onto the charging member while rotating the transport belt. When the liquid or the water droplet is attached onto the transport belt, the resistance value of the charging member may be lowered. Consequently, a current value from a high-voltage power source rises (under the constant voltage control) and a leakage current may be generated.
In a case where a leakage current is generated by attaching liquid onto the transport belt, when the water (liquid) is evaporated, the belt transport device returns to normal operating conditions. However, depending on the type of the liquid, especially, when high viscosity ink which is hardly dried is used, it takes a long time to return to the normal operating conditions because the ink hardly dries.